Structures incorporating nanotubes on a surface of a substrate have been proposed or developed for various applications. For example, such structures can be used in thermal arrays. In particular, arrays that feature excellent absorption properties in wavelengths from the visible to the far infrared can be created.
In various applications, it is desirable to provide structures with selected thermal absorption properties, and that also are relatively robust. For example, energy absorbing materials for incorporation into spacecraft and/or instruments carried by spacecraft are required to be mechanically robust, in order to survive pre-launch cleaning procedures, launch itself, and to provide a suitable service life once deployed. As a further example, energy absorbing materials used on the hulls of surface ships or submarines are preferably capable of maintaining certain minimal levels of energy absorption over extended time periods during deployments at sea. Such energy absorbing materials have included engineered coatings applied to baffles, sensors, external vehicle surfaces, or other surfaces. However, existing materials are often relatively fragile. In addition, improvements in electromagnetic absorption, control over the selectivity of electromagnetic absorption, or control over reflectance, etc., would be desirable.
Various structures have been developed that incorporate nanowires and/or nanotubes. For example, devices incorporating semiconducting single walled carbon nanotube (SWNT) field effect transistors (FETs) have been used in combination with semiconducting metal oxide nanowire sensors in chemical sensor systems that take advantage of the different redox responses of the different materials for improved selectivity. Other systems have proposed combinations of nanorods, semiconducting nanowires, and nano-particles in solar cells. In at least some of these systems, free standing silicon nanowires have been combined with a polymer incorporating carbon nanotubes. However, the performance of such structures in connection with electromagnetic absorption is limited. In particular, the use of a polymer containing nanotubes can exhibit less than desirable thermal properties. In addition, such compositions promote the scattering and reflection of light, which is an undesirable feature for light absorbing applications.
Still other systems have been proposed that utilize silicon wire arrays for solar energy harvesting applications. Such arrays have been reported as providing up to 96% peak absorption. However, various applications require even greater absorption characteristics. Alternatively, systems have been proposed that use carbon nanotubes to increase the efficiency of solar cells. Moreover, systems that combine a film of carbon nanotubes and an array of silicon nanowires have been proposed for use in photoelectron chemical cells. However, the electromagnetic absorption and thermal characteristics of such devices is not sufficiently high for certain applications. In addition, systems that incorporate nanotube structures can be vulnerable to damage.